1. Field of the Invention
The present invention relates to wire dot printer head and wire dot printer.
2. Discussion of the Background
A wire dot printer head performs printing by oscillation of an armature connected to a printing wire between a printing position and a standby position, and when the armature oscillates to the printing position, colliding an end of the wire with a print medium such as a print sheet.
In such wire dot printer heads, known is a printer head which performs printing by generating a magnetic circuit to attract the armature from the standby position to the printing position by a magnetic flux generated around the armature by a coil (See Japanese Published Unexamined Patent Application No. 2001-219586). As shown in FIGS. 6 and 7, in such wire dot printer head 100, an armature 102 supporting a printing wire 101 has a support shaft 103, and the armature is rotatable about the support shaft 103. An armature spacer 105 having a notch 104 accommodating the support shaft 103 of the armature 102 is provided on a yoke 106 to generate a magnetic circuit.
Further, a plate 108 to hold the support shaft 103 to regulate movement of the support shaft 103 is provided on the armature spacer 105 via an elastic spacer 107 to fix the position of the support shaft 103 of the armature 102 by an elastic force. By this arrangement, abrasion of the plate 108 by the support shaft 103 of the armature 102 can be prevented, and the position of the support shaft 103 is fixed.
However, in accordance with recent increment in printing speed, the armature 102 oscillates between the printing position and the standby position, e.g., 2500 times/second, which causes severe vibration during printing, and the support shaft 103 as the rotational center of the armature 102 abrades the surface of the yoke 106.
When the abrasion of the surface of the yoke 106 by the support shaft 103 of the armature 102 progresses, the support shaft 103 of the armature 102 is movable and is shifted from the predetermined position, thus the oscillation of the armature 102 becomes unstable. This degrades the printing quality. Further, when the abrasion on-the surface of the yoke 106 progresses, the armature 102 comes into contact with a coil flange, or the support shaft 103 is slightly moved to scrape the notch 104 of the armature spacer 105. This shortens the life of the wire dot printer head 100.